1. Field of the Invention
The present invention relates to paper-making machines, and, more particularly, to a method of determining an amount of air in a fiber suspension in a paper-making machine.
2. Description of the Related Art
Paper-making machines typically include an approach flow system which transports a fiber suspension, such as a wood pulp suspension, to a headbox. The fiber suspension is discharged from an outlet gap of the headbox onto a forming fabric which travels at an operating speed. Water drains through the forming fabric from the fiber suspension to reduce the water content of the fiber suspension.
The presence of air within the fiber suspension causes problems during the manufacture of the paper. First, the air reduces the efficiency of the pump(s) which are used to transport the fiber suspension to the headbox. For example, a fiber suspension with approximately 5% air (by volume) may reduce the efficiency of the pump(s) by as much as 50%. This in turn means that the size of the pump must be increased and power requirements are dramatically increased. Moreover, air within the fiber suspension typically is in the form of tiny air bubbles which tend to attach via adhesion to the fibers within the fiber suspension. When the fiber suspension is discharged onto the forming fabric, these tiny bubbles do not rapidly disengage from the fibers, and interfere with the drainage of water through the forming fabric from the fiber suspension.
For the foregoing reasons, it is thus preferable to remove as much air as possible from the fiber suspension transported to the headbox. A conventional method of determining an amount of air within the fiber suspension is to draw a sample of the fiber suspension and test the fiber suspension at a location remote from the paper-making machine. This procedure is of course time consuming and labor intensive.
What is needed in the art is a method of determining an amount of air within a fiber suspension in a paper-making machine which is fast, reliable, inexpensive and provides almost instantaneous feed back.